Blast hole charge and charging method



M. G. WOODLE ETAL BLAST HOLE CHARGE AND CHARGING METHOD Filed March 20,1959 INVENTOR. MERLYN G. WOODLE RAYMOND J'. BERTIE BY %'4,W779 4 Z MATTORNEYS MY x Jan. 29, 1963 rates atent dfilfiflh i Patented Jan. 29,1963 free 3,975,464 BLAST HQLE HARGE AND (IHARGTNG METHQD Marlyn G.Woodie and Raymond 3'. Bertie, Babbitt, Minn, assignors to ReserveMining Company, Silver Bay, Miriam, a corporation of Minnesota FiledMar. 2d, 1%9. er. No. 8%,694 1 Claim. (Ci. lii223) The invention relatesto the intimate mixing of a plurality of explosive ingredients in ablast hole, and particularly to a novel and improved explosive charge,and methods of charging a Wet blast hole in open pit mining practice.

While the invention can be used to advantage in any type of rock stratablasting involving the use of drill holes of substantial depth wherein acertain amount of water may be encountered (known in the art as Wetholes) it will be described with occasional reference to the mining oftaconite, a so-called low grade ferrous metal ore existing in largequantities in the ore ranges in Minnesota. The taconite occurs in strataat or near the surface, the layers being substantially horizontal or atan acute angle to the surface. In such cases it is customary to make aninitial or development cut of indefinite length, from which box cuts areblasted at spaced intervals along the sides of the development cut.Mining then proceeds from one box cut to the next, parallel to thedevelopment cut, the object of course being to shatter predeterminedvolumes from the vertical face of the development cut into fragmentswhich can be loaded into trucks by power shovels. For greatestefiiciency a preponderating amount of the fragments should be smallenough to be receivable in the throat of a rock crusher for furtherreduction in size.

For some time, in the art of blasting taconite in open pit mining, therehas been extended use of ammonium nitrate with a carbon-containingadditive such as a hydrocarbon oil or a carbonaceous material such ascoal dust, or charcoal granules. Since these mixtures were not believedto be adaptable to wet holes it was necessary to substitute, below thewater level, different and usually considerably more expensive chargessuch as desensitized gelatine or a non-cap-sensitive explosivesurrounded by pellets of trinitrotoluol (TNT).

It was desirable however to provide an intimately mixed charge, and amethod of securing it beneath the water level in a wet hole, and theattainment of this objective constitutes a major object of the presentinvention.

A further object of the invention is to provide a method of charging awet blast hole with a homogeneously mixed, low cost, high densityexplosive load.

Another object of the invention is to provide a simple and eifectivemethod of charging a wet blast hole, which is not necessarily limited tothe use of Water soluble ingredients, but which permits the use ofinsoluble carbonbearing materials such as hydrocarbon oils, oranthracite coal dust, in preferred conjunction with ammonium nitrate, inthe form of prills, for example, and conventionally termed priliedammonium nitrate.

A further object or" the invention is to provide a method of charging awet blast hole with ammonium nitrate in an amount sufiicient to providea saturated aqueous solution of the ammonium nitrate in intimateassociation with a carbon-supplying substance, Whether soluble orinsoluble.

A further object of the invention is to provide a method as defined inthe last preceding paragraph and wherein the carbon-supplying substanceis anthracite coal in comminuted form.

A further object of the invention is to provide a method of charging awet blast hole with ammonium nitrate in aqueous solution in intimateassociation with a carbonsupplying substance of approximately the samespecific gravity as that of the ammonium nitrate solution.

A further object of the invention is to facilitate achievement of theforegoing objects, including securement of an intimate mixture of thecomponents of the explosive material, and solution of the solubleconstituents, by discharge of a current of air beneath the liquidsurface in the blast hole.

Other objects and advantages will be apparent from the study of thefollowing description of several exemplifications of the invention, inconjunction with the accompanying drawings, in which FIG. 1 shows apreviously-known charge distribution in a wet blast hole,

FIG. 2 shows a somewhat enlarged and fragmentary vertical section of awet blast hole, and pictorially indicating a charging method inaccordance with the present invention,

FIG. 3 shows a fragmentary vertical sectional view of the lower part ofa wet blast hole showing another method and means of loading a charge,and

FIG. 4 shows an improved bottom end portion for a compressed airdischarge line.

Referring first to FIG. 1 there is shown a hole loading arrangementpreviously used in a specific location in a taconite bed, involving abalst hol approximately eight or nine inches in diameter and about fortyfeet deep, and having a Water level, for example, at the broken line WW.The hole is preferably formed by a jet piercing tool known in the artand not necessary to describe here. This type of tool pierces the rockby directing a jet of high velocity flame around the base of the tool,heating and cracking the rock, and driving a stream of fine spalled rockfragments upwardly out of the hole. The tool advances at a steady rate,providing a hole of fairly uniform diameter, but the diameter may beincreased, as in the chambered section 10, by holding the jet for asomewhat longer time than in the upper portion of the hole.

In the previous hole charging practice two cartridges 1]. and 12 ofheavy density blasting agent, for example desensitized gelatin, eachabout two feet long and of a diameter such that it could pass throughthe hole, were loaded, end to end, into the chambered area, and freerunning bulk blasting agent such as pelletized trinitrotoluol was pouredin to completely load the chamber. Three additional cartridges 13, 14and 15 of heavy density blasting agent were placed in the column abovethe two in the chambered area. A primer load, or a heavy densitycartridge with an inserted booster was placed at 16 and tied in with aPrimacord detonating fuse. Primacord is a commercially available fusewhich has a tremendously fast burning speed, around twenty thousand feetper second.

Above the cartridge 16, and above the water line WW as shown, the waterwas sealed off with three-inch to six-inch chunks of ammonium nitrate.Above this plug a certain latitude was permitted because the balance ofthe hole was dry, but in one advantageous arrangement a distance ofapproximately eleven feet was filled with ammonium nitrate prills 18 towhich some hydrocarbon fiuid such as fuel oil had been added, followedby a primer cartridge 19. The remainder of the hole to within about twofeet of its top was filled with oil treated ammonium nitrate prills 2.0.The top 21, two or three feet in height, was stemmed with any granularsandy or earthy material, or with tail-ings from the taconitebeneficiation process. The primer cartridge 19 was tied in with thedetonating circuit through the Primacord fuse above mentioned.

As heretofore indicated the presence of water in a wet hole imposed arestriction on the choice of explosive materials in the portion of theblast hole below the water level, including the bottom chamberedportion. While ammonium nitrate is a relatively cheap and efiicientexplosive when combined with a carbon-bearing compound, one of thecheapest of such compounds is carbon in the form of coal dust and thishas been deemed not practical to use in a wet hole since it has not beenpossible to intimately mix it with an ammonium nitrate aqueous solution.Other ingredients, for example hydrocarbon liquids, are neither solublein nor miscible in water, and will settle in layers dependent on gravityand charging methods.

In accordance with the present invention a method will now be disclosedforsimultaneously charging and homogeneously mixing or associating amixture of ingredients to provide a relatively cheap and powerfullyeffective blasting compound, for example a suitable compound includingammonium nitrate, and sugar, starch, anthracite coal dust, or othercarbon-containing solid.

Referring now to FIG. 2, an air pipe 24 (which may be flexible but ihere shown as solid) is inserted do-wn-' wardly into the chamberedportion 25 of the hole. The pipe 24' should reach to below the waterlevel in the hole bottom, as shown. A stream of compressed air ofmoderate intensity, from a source (not shown) is passed through aflexible connector pipe 26, and down through pipe 24 withthe result thatit bubbles through the water in chamber 25, and upwardly through theannular space 26 between the pipe and the blast hole wall. This annularspace is filled'with water up to the'line W--W. The air current will beat a pressure suitably predetermined so that it agi-tates the'water butdoes not expel any water from the blast hole. The pressure of coursewill drop as the air issues from the relatively small pipe into thelarger space outside the pipe.

While the air is thus being introduced to the water, the desiredexplosive compound, in mixed granular form, is poured, for example fromcontainers 27', into the annular space 26, and it drops to the bottominto the water and into chamber 25. It has been determined that thisprocedure assures a homogeneous mixture of the'ingredients.

into an aqueous slurry which increases in solid consistency until thehole fills to the rising water level and becomes, so to speaksolid-saturated, so that further charging pro-. cedure does not affectthe mix. Soluble ingredients will of course dissolve gradually in theliquid up to the limit of' the liquids capacity to dissolve them.Ingredients such as insoluble or immiscible hydrocarbon fluids, orinsoluble solids will not stratify since the air agitation effect willcontinue as long as the slurry has any mobility and 'beyond that pointno stratification takes place.

The escaping air is at such low pressure that it will not interfere withthe pouring procedure, and the pipe may be gradually raised as theliquid level rises so that its lower end remains beneath the surface ofthe slurry. The air current can be shut off and the pipe Withdrawn afterthe solid constituents build up to the water level. Detonating fuses,and primer cartridges may be inserted in the chambered portion prior toexecution of the disclosed method, if such items are to be used in saidchambered portion.

Above the water level any suitable charging arrangement can be used, forexample that disclosed for use above the line W-..W' in FIG. 1.

FIG. 3 shows an embodiment in which we provide a flexible pipe 30 hereshown as made of rubberlike material, having at its lower end a metaltip or nipple 31 several feet long. In this embodiment thecarbon-bearing additive is anthracite coal dust. To minimize thepossibility that the coal dust might be blown out of the hole, at leastin part, if charged in particle form from open boxes or otherwise asshown in FIG. 2, the dust may be furnished in frangible sacks 33 whichare dumped into the water. The sacks may be of material whichdeteriorates rapidly in water, or they may be fractured by rais- 4 ingand lowering the pipe 30 repeatedly to cut or tear the sacks. Anotherexpedientis to dampen the coal dust before charging, although this mightbe a handicap if the coal dust is exposed to freezing conditions whilesitting at ground level.

FIG. 4 shows a metal nipple provides with side perforations 34 whichpermit free air flow and uniform distribution even if the bottom of thenipple becomes clogged with high consistency slurry.

One of the advantages of the present method is that it can be used withany of the explosive mixture-s heretofore known in the blasting art,including both water-soluble and insoluble solids, and miscible orimmiscible liquids. Some of these ingredients suitable for use (eithersingle or in various combinations) with ammonium nitrate, are sugar,glucose, starch, coal, lampblack, charcoal, alcohol, TNT, fuel oil orother hydrocarbon oil.

Another of the definite advantages of the present invention resides inthe fact that the presence of water in a blast hole does not restrictthe choice of the-operator to materials miscible or soluble in water,but'the operator may use any ingredient indicated by the nature of theterrain to be blasted, in the light of economic considerations.

A preferred explosive mixture to be achieved is the combination ofammonium nitrate, which is a relatively cheap explosive ingredient, witha similarly cheap carbonbearing material which is either soluble inwater, orif insoluble, which is of approximately the same specificgravity as a saturated solution of ammonium nitrate. Under either ofthese alternative conditions we have provided an explosive charge for awet hole which will not stratify even if the charge is permitted tostand in the hole for twenty-four hours or more before it is detonated,particularly when the carbon-bearing material happens to be an insolublesolid such as anthracite coal dust, and when the air-agitation method ashereinabove described has been used.

While we are not limited to a specific depth ofwater in the hole weprefer to operate with a'water content such that no'excess water flowsfrom the hole at the end of the charging step, and preferably the uppersurface of the water should be beneath ground level. We have found thatunder'preferred conditions the water content should be such as to leavewhat we have previously termed a We have found that with the abovedescribed charging method the charge in the hole contains more ammoniumnitrate and carbon bearing'additive than with previously known methodsbecause the voids between solid particles are filled with saturatedsolution. 7

It would be entirely feasible to uniformly mix an explosive compoundsuch as hereinabove described in comminuted form so that it could beintroduced through the air pipe and carried below the liquid surface bythe air current, or a slurry of the compound could be mixed at thesurface and poured into the hole in the annular space beside the airpipe.

What is claimed is:

A method of charging a blast hole having water in a bottom end portionthereof, said method comprising introducing an air-carrying pipe intothe hole so that its lower end portion is below the water surface,continuously discharging an air current downwardly through said pipe sothat it escapes upwardly while agitating the water, and, while said aircurrent is being thus discharged, pouring a previously compoundedexplosive mixture of granular ingredients in said hole in the annularspace between said pipe and the inner wall of said hole, whereby saidmix-. ture drops into the agitated water and forms with the water anintimately mixed aqueous slurry, so as to cause the slurry top surfaceto rise, and, while said surface is rising and said pouring continues,withdrawing said pipe upwardly in such manner that its lower and remainsbeneath but near the said top surface.

References Cited in the file of this patent UNITED STATES PATENTSMcFarland -s Mar. 8, 1949 6 Lee et a1 Mar. 8, 1955 Nowak May 24, 1955Aitchison et al May 15, 1956 Edgerton May 22, 1956 Rinkenbach et a1 Dec.24, 1957 Streng et a1. May 28, 1958 Hradel Jan. 6, 1959 Kolbe Sept. 15,1959 Lambert et a] Oct. 11, 1960

